1. Field of the Invention
The present invention has as its object an exhaust device for internal combustion engines, and a process for manufacturing same. The present invention relates more particularly to an exhaust pipe provided with a housing suitable for mounting a measuring sensor and to the process for making such a housing.
2. Discussion of the Invention
The modern internal combustion engines of motor vehicles are equipped with an electronic control system which adjusts the quantity of fuel injected, the quantity of exhaust gas recirculated, etc. on the basis of preprogrammed strategies and as a function of engine operating conditions.
Among the items of information required by the electronic control systems in order to determine the operating conditions and consequently to adapt the quantity of fuel injected (the degree of opening of the EGR valve, etc.) there are included those relating to the composition and/or to the temperature of the exhaust gases and more particularly to the residual oxygen concentration. These items of information relating to the exhaust gases are delivered by appropriate measuring sensors, which are disposed along the path of the exhaust gases.
In the standard case, the measuring sensors with which the exhaust line is equipped are screwed into internally threaded housings traversing the wall of the exhaust pipes, in such a way as to bring the analysis cells into contact with the flow of exhaust gases.
In view of the slight thickness of the walls of the exhaust pipes in current use (between 1.5 and 2 mm on average) relative to the diameters of the holes to be made (more than 20 mm), the internally threaded holes in the standard case are formed by appropriate rings which are attached by welding in openings made through the exhaust pipes (SEFG welding or resistance welding).
It became apparent to the Applicant that reliance on welded rings suffers from disadvantages, and in particular from a large percentage of defects in assembly and leaktightness. In fact, the heating during welding tends to deform the internal threads of the rings, which sometimes has the effect either of preventing the sensor from being screwed in or, on the other hand, of preventing the sensor from being unscrewed. In addition, these deformations affect the leaktightness of the assembly and therefore cause burned gases to leak out or, depending on the operating point of the engine, even air to be sucked in, which proves particularly detrimental to the quality of the measurements, especially when the sensor is an oxygen sensor.